81121920 has 256 divisors, whose sum is σ = 296110080. Its totient is φ = 18698240.

The previous prime is 81121919. The next prime is 81121921. The reversal of 81121920 is 2912118.

It is an interprime number because it is at equal distance from previous prime (81121919) and next prime (81121921).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81121921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 485677 + ... + 485843.

It is an arithmetic number, because the mean of its divisors is an integer number (1156680).

Almost surely, 2^81121920 is an apocalyptic number.

81121920 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81121920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (148055040).

81121920 is an abundant number, since it is smaller than the sum of its proper divisors (214988160).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81121920 is a wasteful number, since it uses less digits than its factorization.

81121920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 223 (or 211 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 24.

The square root of 81121920 is about 9006.7707864695. The cubic root of 81121920 is about 432.8918475340.

The spelling of 81121920 in words is "eighty-one million, one hundred twenty-one thousand, nine hundred twenty".